It is well known to connect together workpieces with interconnecting joint members that are formed using a template that guides a cutting tool.
It is common to form "finger joints" or "box joints" in workpieces from an interlocking pattern of joint elements ("fingers" and "sockets") in which the joint elements are equally sized and repetitively spaced along the edges of the workpieces. The distance between successive joint elements on a particular workpiece is the pitch of the joint.
In my U.S. Pat. No. 4,428,408 that issued Jan. 31, 1984, entitled "Dovetailing Jig", there is disclosed a jig having a plurality of movable guide fingers that collectively serve as a template for cutting joint elements in workpieces. A cutting tool, such as a router having a depending cutting bit extending through an attached guidebush, is moved between the fingers. The guidebush engages the finger surfaces to control movement of the cutting bit. The fingers can be positioned to form joint elements of varying size and spacing as well as joint elements of uniform size and spacing. It is necessary to position the guide fingers individually.
In most existing jig and template equipment to form "finger" joints, the complementary joint elements of a workpiece are cut by offsetting one workpiece from the other by one-half pitch of the joint spacing under a fixed template. This ensures that the edge or outermost finger of one workpiece mates with the edge or outermost socket of the other workpiece to produce a flush alignment of the workpiece edges. In order to properly offset the workpieces, it is necessary to use a movable or adjustable positioning member or stop for positioning of the workpieces with respect to the fixed template and it is vital that the stop be carefully positioned to accurately reflect the offset of one workpiece with respect to the other. This system of moving or adjusting the positioning member in order to form joint members in a second workpiece that are complementary to joint members in a first workpieces generally limits the template that is guiding the cutting tool to a pattern for cutting a single shape and size of joint member. A different template is required to cut each different size or shape of joint member and the positioning member must be carefully adjusted a distance equal to half the pitch of the template being used.
In addition, it is desirable to be able to adjust the tightness of interfit of joint members cut using a template and jig. Generally, a fixed guidebush or collar is fitted about the cutting bit of the router to engage the guide surfaces of the template. The precise size of finished parts is normally achieved by altering the size of the template. All of the world's leading router manufacturers produce various fixed size (outside diameter) template guidebushes. Many also market box joint templates suitable for at least one cutter/guidebush size combination. Provision is not made to adjust template dimensions, guidebush diameters or cutter diameters. The latter three dimensions all have plus/minus manufacturing tolerances, which, when combined with router shaft/bearing wear (commonly called "run-out") leads to products that "on average" provide a good joint fit, i.e. some fits are correct but most are too tight or too loose. A too-tight fit can be overcome by reducing the guidebush diameter by trial and error. However this is a one-time solution for a particular set-up which is nullified if, for instance, a larger diameter cutter is used the next time.